The boys quarterfinalists also have two unseeded players among them. Fifteen-year-old Tommy Paul, who has never been beyond the semifinals of a Grade 4, has beaten two seeds in his first three matches, including his 6-2, 6-4 win over No. 7 seed Luca Corinteli today. Paul, who is now training at L'Academie de Tennis in Boynton Beach, will play No. 2 seed Spencer Papa, who needed three sets to get by unseeded Henry Craig 3-6, 6-1, 6-2.

Papa, a 16-year-old from Edmund, Oklahoma, saved a break point serving at 3-2 in the third set, with Craig chipping in a couple of errors, and when Papa broke him for the third time in the set, Craig lost his chance for the upset. Papa closed the match with an ace, to reach the quarterfinals of the Pan American Closed for the second straight year.

Canadian Brayden Schnur, the No. 5 seed, also reached the quarterfinals for the second year in a row when Dan Kerznerman, the No. 9 seed, retired with a back injury down 4-1 in the first set. Kerznerman was able to play doubles later in the day, serving underhanded.

Schnur will play No. 3 seed Thai Kwiatkowski, who earned a 6-2, 6-3 victory over No. 16 seed Josh Hagar that was much more difficult than the score might indicate.

Top seed Noah Rubin trailed 5-2 in the opening set against unseeded 14-year-old Frances Tiafoe and it was over an hour before he could claim the first set, but Rubin, the 2011 Pan American finalist, finished quickly 7-6(5), 6-1.

Next up for Rubin will be unseeded Roy Lederman, who defeated another member of the USA's 14-and-under World Championship team, No. 11 seed Michael Mmoh, 6-4, 6-3 in just over two hours.

Lederman, who recently committed to Stanford University, was full of praise for his younger opponent.

"Our points were so long," said Lederman. "He's really good, hits the ball really well, it was just a grind. I said to myself, I'm older, if I can stay in the match, I'm going to have a good chance, because he's probably going to be more immature. But he's really, really good. I served well when I needed to, and stayed in the points as long as possible until he made the mistake, and that was the match."

Lederman was up 5-1 in the second set, but said he got a little nervous before a playing a good game to close out the match.

Because he's now earned admission to his dream school, Lederman is playing with less pressure than he felt before.

"I think it's helping my tennis also," said Lederman, a 17-year-old from Miami. "Before I was all stressed. How much scholarship am I going to get, what schools are going to offer me, it was really stressful. My goal has always been to go to Stanford and I didn't want to screw it up. Now I'm playing much looser, I'm enjoying tennis much more."

The doubles quarterfinals will also be played on Thursday, with the top five seeds still alive in the boys draw, and three of the top four seeds remaining in the girls draw.